Ducting system question

[Hollywood3044]

A friend of mine is having a house built. Out of curiousity I went out to check out the duct work. The contractors have the plenum going into the attic and have it sticking up inside the attic about 3 feet and have all the leads going from that location to each room of the house. My question is this: Is this typical or appropriate installation practice?

[Kevin O'Neill]

Depends on the size of the second floor and the lengths of the runs. It also depends on how much the GC is willing to pay him and whether the GC allows room for a more involved duct system.

[REP]

There is not too much wrong with what you said,its what you leave out that will cause the problems.
For instance this set up sounds like it might be flex duct going to the supply registers.Flex duct has to be stright,very tight and as short as possible with metal ells making the bends.It also must be sized for flex which is very differant than metal runs.
What you didn't mention was the return.There should be ducted returns from every room except batrooms and the kitchen.
You also didn't say what the supply plenum was made of.Metal would be the perfered but is most likely ductboard.
So what you told us means nothing,what you left out means everything.

[Hollywood3044]

Well its a 1250sqft home on a slab and its only one story. The runs cannot be more than 40ft long at most. Yes, it is all flex ducting....there are no returns in the rooms...just one large return in the family room area.

[Kevin O'Neill]

40 feet? GAGG!

Too long!

[Hollywood3044]

40 feet? GAGG!

Too long!

Yea I didn't think this design had integrity in mind.

Thanks for replying.

[George2]

Yea I didn't think this design had integrity in mind.

Thanks for replying.

It's got one thing going for that kind of workmanship (if I can call it that), it's cheap.

[genduct]

Just think of the extra surface area of the "home run flex duct system" All that surface that lgains or losses heat and cooling. Heat and cooling that you are spending $$$.00 to produce.
Well at least the unit is in the space so the airhandler/ cabinet leakage isn't as much of a problem.
What your friend needs is a simple trunk duct up there with shorter flex runs